In remote telecommunication installations, it is frequently desired to transfer, in addition to the communication signals proper, switching data signals regarding the operations of the system between individual exchanges. These switching data signals are either signals independent of the respective communication or signals that are associated with the respective communication. In the latter case, such signals are particularly concerned with switching characteristics related to the transmission of the respective communication. In general, such switching signals serve in exchanges to control switching operations, such as the triggering of communications.
To transfer switching data signals in a PCM (pulse code modulated) telecommunication network, it is known in the art to utilize in each case one time slot of a channel within a pulse frame, each comprising one time slot of a time channel from a series of time channels (see "NTZ," 1967, Volume 11, pages 667-682 which is available in the English language). In pulse frames comprising 32 time slots each and having a period of 125 /us, the channel 16 or 17 of the 16th or 17th time channel is frequently employed as a "switching data channel" within the respective pulse frame. All of the information signals are then transferred to the time channels of the information channel.
With reference to the transfer of switching data signals, it is likewise known in the art to utilize the available channel capacity several times. For example, to transfer characteristics concerning individual communications or information within the time slot available in each pulse frame of the respective communication, one time element of the 8 available time elements is employed (see "Elektrisches Nachrichtenwesen," Volume 42, No. 2, 1968, pages 125-135 and Electrical Communication, Volume 43, 2, 1968, pages 123 through 129). By developing main frames comprising 4 pulse frames each, a multiplicity of different characteristics or data are transferred per communication.
To carry out or at least to trigger operations determined by the respective switching data signals, it is necessary to provide for corresponding switching data receiving/transmitting devices in the exchanges of the telecommunication network. These receiving/transmitting devices are elaborate and complicated, particularly, if a comparatively heavy traffic is to be developed in the exchange with which said devices are associated and if the respective exchange is connected to other exchanges of the telecommunication network via a multiplicity of junction lines.
A related problem results, if the traffic capacity of an exchange is to be enlarged. It then becomes necessary to either construct the switching data receiving/transmitting devices with a view to the maximum junction traffic to be expected, or to reconstruct the respective signal receiving/transmitting equipment in accordance with the data available in each case. Both solutions are unsatisfactory, however. In the first solution, the disadvantage resides in the fact that in the basic expansion of an exchange, wherein the respective exchange does not yet have to cope with the junction traffic to be overcome in the final expansion, an extensive circuitry has to be provided in advance, so as to be able to overcome the maximum junction traffic to be expected. The second solution has the disadvantage that with each increase in the traffic load of the exchange the switching data receiving/transmitting equipment has to be replaced entirely by other receiving/transmitting equipment that would meet the increased requirements.
An object of this invention is therefore, to provide apparatus for receiving and transmitting switching data signals formed particularly by switching characteristics associated with communications in or from an exchange of a telecommunication network without necessitating a comparatively costly reconstruction of the receiving/transmitting equipment, when the traffic load of the exchange in question is changed.